Study of shear wave velocity structure of the crust beneath the Andaman Island through joint inversion of the teleseismic receiver function and Rayleigh wave group velocity measurements from 10 broadband seismographs over the Island revealed continent-like crust beneath, possibly the Burma continental crust. The subducting Indian plate may lie down below this overriding plate.
Study of the uppermost mantle velocities and dip of Indian Moho beneath the NW Himalaya and Ladakh using 42 regional waveform data recorded on 15 seismographs along a ~600 km-long profile show that the Indian Moho is underthrusting at a shallow angle (~2.58º) beneath the Himalaya, steepens abruptly (~6.68º) further north of the Southern Tibetan Detachment and continues at a shallow angle (~3.88º) beneath Ladakh. Seismic velocity discontinuities in the upper mantle in the depth range of 200 to 800 km beneath the western Himalaya from Gangetic Plain (27.5ºN latitude) to Ladakh-Karakoram region (35ºN latitude) is detected and thickened mantle transition zone (~255-262 km) is observed beneath Gangetic Plain and NW Himalaya compared to the Tibetan Himalaya due to presence of cold material within (~100º C less than normal).
The Eastern Ghat Mobile Belt (EGMB), a tectonically active area extends along the eastern margin of Peninsular India, is divided into three provinces, namely, Eastern Ghat Province, the Jeypore Province, and the Krishna Province. The Ongole domain of Krishna Province in the Eastern Ghat Mobile Belt is a seismically active region that has experienced four moderate earthquakes of magnitude ≥5.0, of which largest one is of magnitude 5.4 occurred on 27th March 1967. Significant crustal thickness variation and a low velocity layer of variable thickness and velocities 3.54–3.7 km/s) is observed in the region which may indicate presence of fluids in the crust, which also be one of the causes of the intraplate earthquakes in the study region.
Earthquake generation in the intraplate setting of Saurashtra has been attributed to a ~NNE–SSW trend (swarm type) and a ~NW trending zone of higher Vp and higher Vp/Vs, possibly indicating a zone of crystallized mafic magma, which was transported from deeper Earth (moderate ones). The latter represents a pronounced heterogeneity and provides locale for stress accumulation in this region. After 2001 Bhuj earthquake (Mw 7.7), due to stress perturbation the ~NNE–SSW trending fault got activated and caused bigger earthquakes in this region. Moreover, the crystallized mafic magma is possibly feeding fluids at shallower depths for causing the swarm-type earthquake activities in this region.
Local site conditions (i.e., thickness of sediments) have been determined in the central part of the Indo- Ganga Plains, which are responsible for ground motion amplification using seismological data from 42 broad band and strong motion velocity meters together with magnetotelluric data obtained along 6 profiles. The sedimentary thickness varies from few hundred meters to about 4 km. The dominant frequencies in the central Ganga plains at various site vary between 1 s to about 7 s. These dominant frequencies affect the tall buildings. Calculations based on reasonable earthquake source and attenuation models and application of random vibration theory suggest that peak ground acceleration and peak ground velocity at soft sites near the foothills, located 100 km from the epicenter, would be amplified by a factor of 2–4 and 6–12, respectively. Such estimates allow the civil engineers and agencies like the National Disaster Management Authority, Bureau of Indian standards to estimate the risk of vulnerable built in environment of this region.
Discrimination of manmade Explosions and Earthquakes is very important and have been carried out on the basis of Pn/Lg and Pn/Sn amplitude ratios of the explosion and earthquake waveforms, which exhibit distinct differences in the higher frequency window. Applications to data from the 11th May, 1998 Pokhran underground nuclear explosion (NE) with those of an earthquake (EQ) of comparable magnitude that occurred in its vicinity (~100 km west) on 9th April, 2009, has generated unambiguous affirmation of the technique.
|Dr. Ramesh D. S (on deputation to IIG, Mumbai)||Chief Scientist|
|Dr. Satyanarayana H. V. S||Chief Scientist|
|Dr. Sandeep Kumar Gupta||Senior Scientist|
|Dr. Sivaram K||Senior Scientist|
|Mr. Satish Kumar K||Senior Scientist|
|Mr. Sudesh Kumar||Scientist|
|Mr. C. H. Nagabhushana Rao||Scientist|
|Mr. Srinivas K. N S. S. S||Senior Technical Officer (1)|
|Mr. Srihari Rao M||Technical Officer|
|Mr. Pavan Kishore P||Technical Officer|
|Mr. Prasad B. N. V||Technical Officer|
|Mr. Ashok Kumar Sharma||Technical Officer|
|Mr. Agamaiah T||Multi Tasking Staff|
Page Last Updated On : 24-05-2018